1. Field of the Invention
The present invention relates to a musical sound waveform generator in an electronic musical instrument and more particularly to a musical sound waveform generator for generating a musical sound waveform including a lot of higher harmonics components, such sound being produced by performing a modulation, and also to a method for generating such musical sound waveform.
The present invention further relates to a musical sound waveform generator and a method for generating a musical sound waveform for controlling a characteristic of a musical sound waveform based on the manner in which the instrument is played.
The present invention further relates to a musical sound waveform generator for producing a musical waveform by generating a modulated waveform signal with a multi-stage process and using a discretional combination of connections of these processes, and to a method for producing the musical waveform.
The present invention further relates to a musical waveform generator for producing a stereo musical waveform containing a lot of higher harmonics components and subjected to a modulation.
2. Description of the Prior Art
As a first prior art of an electronic musical instrument capable of digitally producing a musical waveform containing various kinds of complex characteristics, an electronic musical instrument using an FM method recited in, for example, Japanese Patent Publication Sho 54-33525 or Japanese Patent Early Disclosure Sho 50-126406 is cited.
As a musical sound waveform, this method basically uses a waveform output e obtained by the following operation equation. EQU e=A.multidot.sin {.omega.ct+I(t) sin .omega.mt} (1)
A carrier frequency .omega..sub.c and a modulation waveform frequency .omega..sub.m for modulating the carrier frequency .omega..sub.c are selected in an appropriate ratio. In addition, a modulation depth function I(t) and an amplitude coefficient A, both of which vary with time, are provided. This enables composition of a musical sound with complex and time-variable harmonics characteristics similar to that of an actual musical instrument, and also of a highly individual composite musical sound.
As a second prior art system obtained by improving the FM method, an electronic musical instrument disclosed in Japanese Patent Publication Sho 61-12279 is provided. This method uses a triangular wave arithmetic operation in place of the sine arithmetic operation shown in equation (1). The musical waveform output e is obtained from the following equation. EQU e=A.multidot.T {.alpha.+I (t) T (.theta.)} (2) )
T(.theta.) is a triangular wave function produced by a modulation wave phase angle .theta.. A carrier wave phase angle .alpha. and a modulation wave phase angle .theta. are advanced at an appropriate proceeding speed ratio. A modulation depth function I(t) and an amplitude coefficient A are provided in a manner similar to that in the first prior art example, thereby composing a musical sound waveform.
The musical sound of an actual musical instrument such as a piano contains in addition to a fundamental wave component based on a pitch frequency, harmonics components having a plurality of frequencies of an integer times the fundamental wave component and a fairly higher harmonics component. Further, a harmonics component comprising a non-integer times the fundamental wave is sometimes included. These harmonics components give a musical sound a rich quality. The musical sound of an actual musical instrument gradually fades after initial production. The amplitude of the harmonics components decrease first starting with the higher harmonic components, until finally only a single sine wave component corresponding to the pitch frequency remains. Musical sounds which originally include only a single sine wave component also exist.
In the first prior art mentioned above, a modulation by a sine wave is treated as a basic approach. Therefore, the value of the modulation depth function I(t) in equation (1) reduces to near 0 with time, thereby realizing a process in which a musical sound is attenuated so that it comprises only a single sine wave component or a musical sound comprising only a sine wave component is generated, as is similar to an actual musical sound. However, the musical sound generated in accordance with equation (1) has a frequency component concentrated in a lower harmonics component (i.e. a lower frequency component). By making a value of a modulation depth function I(t) large, a deep modulation is applied but a suitable higher harmonic component (i.e. a higher frequency component) is not produced. Therefore, the above first prior art has the problem that it cannot produce a musical sound with a rich quality similar to that of an actual musical instrument, and that the quality of a musical sound which it can generate is limited.
By contrast, in the second prior art based on equation (2), a modulation by a triangular wave originally containing various harmonics is used as the fundamental approach. Therefore, the second prior art can easily produce a musical sound in which a higher harmonics component clearly exists as a frequency component. However, equation (2) does not contain a single sine wave component term. Therefore, it has the problem that it cannot realize a process in which a musical sound is attenuated to have only a single sine wave component or a musical sound comprising only a single sine wave component is generated, as is similar to an actual musical sound.
An acoustic musical instrument such as a piano can produce a musical sound containing many higher harmonics components, thus providing a hard feeling, if a key is depressed at high speed. Conversely, it can produce a musical sound containing only a single sine wave component, thus providing a soft feeling, if a key is depressed extremely slowly.
However, if a keyboard-type musical instrument with the above effect is intended to be realized by using the first prior art, a higher harmonics component does not normally appear in a musical sound produced by equation (1) recited above. As a result, even if the value of the modulation depth function I(t) is controlled to be large upon a quick key depression, the level of the higher harmonics components produced are limited Therefore, there is the problem that a musical sound containing many higher harmonics corresponding to a performance operation cannot be produced.
In contrast, when a keyboard having the above effect is intended to be realized by the second prior art, a musical tone comprising only a single sine wave component cannot be produced as stated above. As a result, there is a problem that, even if a modulation depth function I(t) is controlled to be small, for example 0, upon an extremely weak key depression, a control for producing only a single sine wave component, and thus a musical sound with a soft feeling, is impossible.
Further, in the first and second prior art, sometimes a waveform of a sufficient frequency characteristic cannot be obtained by merely providing a waveform output e through a single arithmetic operation as shown by equations (1) and (2). Therefore, these operations can be executed by performing a plurality of predetermined connections and combinations. A waveform output can be obtained by an arithmetic operation in the previous stage and inputted in place of I(t)sin .omega.t or I(t)T(.theta.) of equations (1) or (2). Such a prior art, in which a sound waveform of a more complex harmonics structure can be composited, is disclosed in Japanese Patent Disclosure Sho 58-211789.
However, where the first prior art is applied to the prior art in which a waveform outputting operation based on a modulation is executed a plurality of times by performing a predetermined connection and combination, a complex connection and combination is necessary to obtain sufficient harmonics components. This is because it is difficult to produce a higher harmonics component with the first prior art. Therefore, when the first prior art is applied to a low-priced musical instrument in which the above connection and combination is limited, a musical sound with a rich sound quality like an actual musical sound cannot be produced and the sound quality of the generated musical sound is limited.
Where the second prior art is applied to the prior art in which a plurality of waveform outputting operations based on a modulation are executed by a predetermined connection and combination, there is an advantage that sufficient harmonics components can be obtained by a relatively simple connection and combination. Conversely, however, there is a problem that a waveform output of a single sine waveform component or a sine wave composite signal such as the musical sound of a hammond organ obtained by parallelly mixing a plurality of single sine wave outputs with different frequencies cannot be obtained and that the sound quality of the musical sound which is able to be produced is limited.
As stated above, in the prior art in which a plurality of waveform output operations based on a modulation is executed by a predetermined connection and combination, a modulation method is not particularly limited. As a result it is easy to perform a musical sound composition comprising a single sine wave component, but it is difficult to obtain a sufficient harmonics component by a simple connection and combination if merely the first musical sound waveform generating method is used. But, when only the second musical sound waveform generating system is used, sufficient harmonic components can be obtained by a simple connection and combination, but a musical sound such as a single sine wave component is difficult to compose. The prior art has mutually contradicting problems.
As a result, when a musical sound generation is conducted based on a combination technology without limiting the modulation method, a musical sound waveform containing many harmonics components immediately after initial production, which gradually fade with time so that only a sine wave component remains, cannot be obtained by simple connection and combination. Therefore, there is a problem that a good musical sound quality cannot be produced in an inexpensive electronic musical instrument.
The frequency structure of respective higher harmonics often differs depending on the kind of musical instrument. Therefore, it is desirable to generate a musical sound with various harmonics structures. However, in the first prior art, a sine wave is driven by a sine wave. Therefore, only a musical sound with a harmonics characteristics produced by a combination of sine waves can be generated. Further, as stated above, it is difficult to produce higher harmonics. Therefore, the tone of the musical sound which can be produced is limited. On the other hand, in the second prior art, a triangular wave is driven by a triangular wave. Therefore, only a musical sound with a harmonics characteristics produced by a combination of the triangular waves can be generated. Therefore, the kind of a musical sound which can be generated is limited.
In addition to the various problems stated above, in order to produce a stereo effect in a musical sound waveform generator of the modulation type as stated above, a musical sound signal is conventionally delayed by a delay element such as a BBD or a RAM. The delay period is independently controlled by respective left and right stereo channels, thereby producing a stereo musical sound signal to provide a stereo effect.
However, the above prior art has a problem that it needs a delay apparatus in addition to an ordinary musical sound generator to obtain a stereo effect, thereby increasing the cost of the entire apparatus.